Am 03.07.2012 15:20, schrieb Paolo Bonzini:
> Introduce a new feature bit and configuration field that provide
> support for toggling the cache mode between writethrough and writeback.
>
> Also rename VIRTIO_BLK_F_WCACHE to VIRTIO_BLK_F_WCE for consistency with
> the spec.
My spec (and my kernel as well) call it VIRTIO_BLK_F_FLUSH.
What's the status of the kernel and spec side of the change?
>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> hw/virtio-blk.c | 16 ++++++++++++++--
> hw/virtio-blk.h | 4 +++-
> 2 files changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
> index fe07746..280f96d 100644
> --- a/hw/virtio-blk.c
> +++ b/hw/virtio-blk.c
> @@ -510,9 +510,19 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
> blkcfg.size_max = 0;
> blkcfg.physical_block_exp = get_physical_block_exp(s->conf);
> blkcfg.alignment_offset = 0;
> + blkcfg.wce = bdrv_enable_write_cache(s->bs);
> memcpy(config, &blkcfg, sizeof(struct virtio_blk_config));
> }
>
> +static void virtio_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
> +{
> + VirtIOBlock *s = to_virtio_blk(vdev);
> + struct virtio_blk_config blkcfg;
> +
> + memcpy(&blkcfg, config, sizeof(blkcfg));
> + bdrv_set_enable_write_cache(s->bs, blkcfg.wce != 0);
> +}
We need to call bdrv_flush() here when turning WCE off. And it seems we
don't have a way to signal failure, or may we just leave the bit unchanged?
> @@ -49,6 +50,7 @@ struct virtio_blk_config
> uint8_t alignment_offset;
> uint16_t min_io_size;
> uint32_t opt_io_size;
> + uint8_t wce;
> } QEMU_PACKED;
If the spec isn't set in stone yet, we could make it a flags field
instead of using a whole byte for a single flag.
Kevin
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